The main advantage of the 9 vs. the 7 is binaural processing, which gives you more of a 3d effect or surround sound. Instead of just two microphones, you’ve got 4 working together. That’s going to help you hear better in noisy situations.
I work more with Oticon, and their equivalent model is the Alta. I had one patient who upgraded from a Phonak Audeo to the Alta, and he said he could tell a big difference in noisy environments.